The present invention relates to the art of earth boring and, more particularly, to an earth boring bit adapted for boring in varying formations. The present invention is ideally suited for boring relatively large diameter holes.
A need exists for an earth boring bit that will operate effectively in a wide range of formations and that will bore a relatively large diameter hole. Provisions must be made for removing the drill cuttings from the borehole as the drilling operations proceed. For example, the ongoing construction of the Alaskan pipeline involves the boring of holes at periodic intervals through the tundra, permafrost and varying formations, and the grouting-in of long piles upon which elevated supports will be constructed to suspend the pipeline above the surface of the ground.
The environment for the boring of the aforementioned holes is extremely hostile, both because of the climate conditions and the geological conditions. Due to the destructive effect heavy vehicles have on the tundra, construction of the pipeline is limited to the time during the winter months when the tundra is frozen hard and less susceptible to damage from the heavy vehicles. The extreme cold affects properties of men, machines and materials and hampers drilling conditions. Metals which are tough and strong at normal temperatures become brittle and weak at the extremely low temperatures encountered. Motor oil turns into an almost solid mass. Elastomerics and plastics for the most part become brittle and weak.
The geological formations encountered in the boring of the aforementioned holes require a bit that is adapted for drilling through a wide range of formation characteristics. In many places the formations consist of unconsolidated materials involving large boulders, frozen and unfrozen water and other adverse conditions. Because the same bit will be used to drill a large number of holes along a length of the pipeline, the bit will be expected to encounter widely varying drilling conditions. The drill cuttings and debris must be removed from the borehole and properly controlled to prevent contamination of the environment. The drill cuttings must be lifted off bottom in order that they may become entrained with the flow of fluid through the drill string. The wall of the borehole must remain intact even in the presence of intruding water.
Conventionally, drilling is conducted by forcing a drilling fluid downward through the interior of the drill string wherein it passes through a multiplicity of nozzles passing onto or adjacent to the cutters to the bottom of the borehole, gathering cuttings and debris and carrying the cuttings and debris upward in the annulus between the wall of the drill string and the wall of the borehole. The drilling fluid may be air or some type of liquid drilling mud. An example of this type of drilling is shown in U.S. Pat. No. 3,087,558 to W. J. Dougherty, Jr., patented Apr. 30, 1963. It is also known to drill by what is known as a reverse circulation drilling system. This type of system is described in U.S. Pat. No. 3,416,617 to W. D. Elenburg patented Dec. 17, 1968. Drilling fluid is forced downward between the walls of dual concentric drill pipes until it reaches the bottom of the well bore and subsequently travels upward in the central annulus of the drill string carrying the cuttings and debris to the surface.